Invoice email is sent twice

Could this be related to 🐛 Order onPaid event called twice RTBC ?

Seems working as expected & this implementation will allow any more complex isolated logic in future if needed.
LGTM!

Potentially a duplicate of 🐛 mail attachment not included Closed: won't fix , perhaps we should consider queueing the email too, will come back to this either later today or on Friday.

From my live experience, this double send (once at confirmation and another time when marked as fully paid) is not an issue.
On different scenario, I understand it may be.

Shall we need one more checkbox inside "/admin/commerce/config/invoice-types/TYPE/edit" > Emails ?

NOW:
  [ ]  Email the customer a confirmation when an invoice is "confirmed" or paid

THEN:
  [ ]  Email the customer a confirmation when an invoice is confirmed 
  [ ]  Email the customer a confirmation when an invoice is paid

From my live experience, this double send (once at confirmation and another time when marked as fully paid) is not an issue.
On different scenario, I understand it may be.

In some cases, it might make sense to send it twice... The invoice status might affect the invoice content, for example a "Paid" mention could be appended.

Having different checkboxes wouldn't really help as it could be the email should still be sent on both transitions, and some invoices could be sent on confirm, others on paid?

I was actually starting to fix this, but now having second thoughts..

Since this was reported in 🐛 mail attachment not included Closed: won't fix , I'm guessing the consensus is that the same email should not be sent twice.

I agree the flow and user expectation is not completely clear.

Where is the commerce invoice workflow described?

I went ahead and committed a slightly different patch.

"Having different checkboxes wouldn't really help as it could be the email should still be sent on both transitions, and some invoices could be sent on confirm, others on paid?"

Having 2 checkboxes would help when I have 3 differents projects:

project A: owner needs to send a mail when a new order is confirmed
project B: owner needs to send a mail when a new order is confirmed and later on once a payment is received
project C: owner needs to send a mail when a order is paid.

We need flexibility. Maybe even flexibility more that #8 cases.